[petsc-users] issues with VecSetValues in petsc 3.19

Matthew Knepley knepley at gmail.com
Fri May 5 04:26:23 CDT 2023 

On Fri, May 5, 2023 at 5:13 AM Edoardo alinovi <edoardo.alinovi at gmail.com>
wrote:

> Hi Matt,
>
> I have some more questions on the fieldsplit saga :)
>
> I am running a 1M cell ahmed body case using  the following options:
>
>     "solver": "fgmres",
>     "preconditioner": "fieldsplit",
>      "absTol": 1e-6,
>      "relTol": 0.0,
>
>     "options":{
>        "pc_fieldsplit_type": "multiplicative",
>        "fieldsplit_u_pc_type": "ml",
>        "fieldsplit_p_pc_type": "ml",
>        "fieldsplit_u_ksp_type": "preonly",
>        "fieldsplit_p_ksp_type": "preonly",
>        "fieldsplit_u_ksp_rtol": 1e-2,
>        "fieldsplit_p_ksp_rtol": 1e-2,
> }
>
>
> I have run the case using -ksp_monitor_true_residual and this is the
> results I am getting:
>
>
>   Residual norms for UPeqn_ solve.
>   0 KSP unpreconditioned resid norm 5.003190920461e+00 true resid norm
> 5.003190920461e+00 ||r(i)||/||b|| 4.993739374163e-03
>   1 KSP unpreconditioned resid norm 4.959389845148e+00 true resid norm
> 4.959389845148e+00 ||r(i)||/||b|| 4.950021043622e-03
>   2 KSP unpreconditioned resid norm 4.793097370730e+00 true resid norm
> 4.793097370730e+00 ||r(i)||/||b|| 4.784042712927e-03
>   3 KSP unpreconditioned resid norm 4.187770916162e+00 true resid norm
> 4.187770916162e+00 ||r(i)||/||b|| 4.179859782782e-03
>   4 KSP unpreconditioned resid norm 3.099045576565e+00 true resid norm
> 3.099045576565e+00 ||r(i)||/||b|| 3.093191158212e-03
>   5 KSP unpreconditioned resid norm 2.072551338956e+00 true resid norm
> 2.072551338956e+00 ||r(i)||/||b|| 2.068636074628e-03
>   6 KSP unpreconditioned resid norm 1.414678932482e+00 true resid norm
> 1.414678932482e+00 ||r(i)||/||b|| 1.412006457328e-03
>   7 KSP unpreconditioned resid norm 1.006854855789e+00 true resid norm
> 1.006854855789e+00 ||r(i)||/||b|| 1.004952802592e-03
>   8 KSP unpreconditioned resid norm 7.332800358083e-01 true resid norm
> 7.332800358084e-01 ||r(i)||/||b|| 7.318947938062e-04
>   9 KSP unpreconditioned resid norm 5.406076142092e-01 true resid norm
> 5.406076142093e-01 ||r(i)||/||b|| 5.395863503846e-04
>  10 KSP unpreconditioned resid norm 4.037336888099e-01 true resid norm
> 4.037336888100e-01 ||r(i)||/||b|| 4.029709940193e-04
>  11 KSP unpreconditioned resid norm 3.041388930530e-01 true resid norm
> 3.041388930530e-01 ||r(i)||/||b|| 3.035643431559e-04
>  12 KSP unpreconditioned resid norm 2.299815364065e-01 true resid norm
> 2.299815364066e-01 ||r(i)||/||b|| 2.295470774436e-04
>  13 KSP unpreconditioned resid norm 1.739866268817e-01 true resid norm
> 1.739866268817e-01 ||r(i)||/||b|| 1.736579481074e-04
>  14 KSP unpreconditioned resid norm 1.317133652074e-01 true resid norm
> 1.317133652074e-01 ||r(i)||/||b|| 1.314645450067e-04
>  15 KSP unpreconditioned resid norm 9.966247212017e-02 true resid norm
> 9.966247212019e-02 ||r(i)||/||b|| 9.947419937897e-05
>  16 KSP unpreconditioned resid norm 7.531138284402e-02 true resid norm
> 7.531138284404e-02 ||r(i)||/||b|| 7.516911183479e-05
>  17 KSP unpreconditioned resid norm 5.646770286889e-02 true resid norm
> 5.646770286889e-02 ||r(i)||/||b|| 5.636102952452e-05
>  18 KSP unpreconditioned resid norm 4.225114444838e-02 true resid norm
> 4.225114444838e-02 ||r(i)||/||b|| 4.217132765661e-05
>  19 KSP unpreconditioned resid norm 3.160393382046e-02 true resid norm
> 3.160393382046e-02 ||r(i)||/||b|| 3.154423071329e-05
>  20 KSP unpreconditioned resid norm 2.366499890335e-02 true resid norm
> 2.366499890334e-02 ||r(i)||/||b|| 2.362029326721e-05
>  21 KSP unpreconditioned resid norm 1.759504138840e-02 true resid norm
> 1.759504138839e-02 ||r(i)||/||b|| 1.756180253124e-05
>  22 KSP unpreconditioned resid norm 1.309326628086e-02 true resid norm
> 1.309326628085e-02 ||r(i)||/||b|| 1.306853174355e-05
>  23 KSP unpreconditioned resid norm 9.710513089816e-03 true resid norm
> 9.710513089808e-03 ||r(i)||/||b|| 9.692168923954e-06
>  24 KSP unpreconditioned resid norm 7.171039760236e-03 true resid norm
> 7.171039760227e-03 ||r(i)||/||b|| 7.157492922743e-06
>  25 KSP unpreconditioned resid norm 5.277221846963e-03 true resid norm
> 5.277221846949e-03 ||r(i)||/||b|| 5.267252627824e-06
>  26 KSP unpreconditioned resid norm 3.906960734588e-03 true resid norm
> 3.906960734575e-03 ||r(i)||/||b|| 3.899580080737e-06
>  27 KSP unpreconditioned resid norm 2.896843259283e-03 true resid norm
> 2.896843259273e-03 ||r(i)||/||b|| 2.891370822059e-06
>  28 KSP unpreconditioned resid norm 2.140269358580e-03 true resid norm
> 2.140269358568e-03 ||r(i)||/||b|| 2.136226167881e-06
>  29 KSP unpreconditioned resid norm 1.585513255966e-03 true resid norm
> 1.585513255956e-03 ||r(i)||/||b|| 1.582518057055e-06
>  30 KSP unpreconditioned resid norm 1.173839272299e-03 true resid norm
> 1.173839272299e-03 ||r(i)||/||b|| 1.171621768229e-06
>  31 KSP unpreconditioned resid norm 8.777233482545e-04 true resid norm
> 8.777233482544e-04 ||r(i)||/||b|| 8.760652378615e-07
>  32 KSP unpreconditioned resid norm 6.546689191353e-04 true resid norm
> 6.546689191370e-04 ||r(i)||/||b|| 6.534321816833e-07
>  33 KSP unpreconditioned resid norm 4.973281362004e-04 true resid norm
> 4.973281362015e-04 ||r(i)||/||b|| 4.963886317973e-07
>  34 KSP unpreconditioned resid norm 3.775325682448e-04 true resid norm
> 3.775325682480e-04 ||r(i)||/||b|| 3.768193700902e-07
>  35 KSP unpreconditioned resid norm 2.908052735383e-04 true resid norm
> 2.908052735387e-04 ||r(i)||/||b|| 2.902559122310e-07
>  36 KSP unpreconditioned resid norm 2.239556213185e-04 true resid norm
> 2.239556213218e-04 ||r(i)||/||b|| 2.235325459370e-07
>  37 KSP unpreconditioned resid norm 1.698373081988e-04 true resid norm
> 1.698373081996e-04 ||r(i)||/||b|| 1.695164679184e-07
>  38 KSP unpreconditioned resid norm 1.277467123301e-04 true resid norm
> 1.277467123333e-04 ||r(i)||/||b|| 1.275053855510e-07
>  39 KSP unpreconditioned resid norm 9.506326626848e-05 true resid norm
> 9.506326626983e-05 ||r(i)||/||b|| 9.488368190523e-08
>  40 KSP unpreconditioned resid norm 7.223958235163e-05 true resid norm
> 7.223958235336e-05 ||r(i)||/||b|| 7.210311429367e-08
>  41 KSP unpreconditioned resid norm 5.509671615415e-05 true resid norm
> 5.509671615512e-05 ||r(i)||/||b|| 5.499263274677e-08
>  42 KSP unpreconditioned resid norm 4.189229263778e-05 true resid norm
> 4.189229263744e-05 ||r(i)||/||b|| 4.181315375394e-08
>  43 KSP unpreconditioned resid norm 3.067856645608e-05 true resid norm
> 3.067856645894e-05 ||r(i)||/||b|| 3.062061146665e-08
>  44 KSP unpreconditioned resid norm 2.340298386078e-05 true resid norm
> 2.340298386081e-05 ||r(i)||/||b|| 2.335877319825e-08
>  45 KSP unpreconditioned resid norm 1.791143784234e-05 true resid norm
> 1.791143784276e-05 ||r(i)||/||b|| 1.787760127991e-08
>  46 KSP unpreconditioned resid norm 1.355654057227e-05 true resid norm
> 1.355654057087e-05 ||r(i)||/||b|| 1.353093086041e-08
>  47 KSP unpreconditioned resid norm 1.020861247518e-05 true resid norm
> 1.020861247732e-05 ||r(i)||/||b|| 1.018932735009e-08
>  48 KSP unpreconditioned resid norm 7.642335784085e-06 true resid norm
> 7.642335784452e-06 ||r(i)||/||b|| 7.627898619923e-09
>  49 KSP unpreconditioned resid norm 5.874756954976e-06 true resid norm
> 5.874756956850e-06 ||r(i)||/||b|| 5.863658931960e-09
>  50 KSP unpreconditioned resid norm 4.512356844825e-06 true resid norm
> 4.512356846552e-06 ||r(i)||/||b|| 4.503832536701e-09
>  51 KSP unpreconditioned resid norm 3.438985239280e-06 true resid norm
> 3.438985240743e-06 ||r(i)||/||b|| 3.432488641125e-09
>  52 KSP unpreconditioned resid norm 2.655998139390e-06 true resid norm
> 2.655998140374e-06 ||r(i)||/||b|| 2.650980684556e-09
>  53 KSP unpreconditioned resid norm 2.051081181832e-06 true resid norm
> 2.051081181929e-06 ||r(i)||/||b|| 2.047206476954e-09
>  54 KSP unpreconditioned resid norm 1.581756364000e-06 true resid norm
> 1.581756364725e-06 ||r(i)||/||b|| 1.578768262982e-09
>  55 KSP unpreconditioned resid norm 1.207420527415e-06 true resid norm
> 1.207420527996e-06 ||r(i)||/||b|| 1.205139585453e-09
>  56 KSP unpreconditioned resid norm 9.377914349033e-07 true resid norm
> 9.377914347157e-07 ||r(i)||/||b|| 9.360198494806e-10
>
> I have the feeling I am self-inflicting some overhead not using relative
> tolerance (if I set 1e-3 I converge in 8 iters vs 56...), however I would
> like to ask the following question:
>
> From your point of view, is this a reasonably convergence history?
>

It is steadily converging. It is hard to say what is achievable without
really understanding the problem.

You could imagine trying some variants:

  - Using "richardson" or "gmres" instead of "preonly" on the inner solvers

  - Using Schur complement instead of multiplicative if you had a decent
approximation matrix for the Schur complement

  Thanks,

     Matt


> Thank you!
>


-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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